During the 1980's (and I believe since) speed trials were held annually at Portland, Dorset, UK. The 'course' originally consisted of a series of buoys set in a 1nm diameter circle. A run constituted entering the circle via one pair of buoys and exiting via the corresponding pair, directly opposite. This was later refined to a 'bow-tie' shaped layout either side of 90degrees to the wind allowing boats to choose their best course for sheer speed between a close reach and a broad reach. It is many years since I visited a speed week, but the camaraderie and enjoyment of comparing approaches to a common goal was very memorable. I don't know exactly what timing method was employed but I do know that 'gate boats' were involved.

With modern portable GPS's it should be possible to arrange a set of buoys, entered as waypoints on several GPS units. Then each boat could carry such a unit for their run and hand it over to a support boat at the end of the run for their attempt to be downloaded to a laptop before the GPS unit is passed over to another competitor.

Alternatively, if the distance between buoys is known exactly, synchronised watches on two properly stationed gate boats plus a radio link is all that is required (plus some mathematics).

Just my twopenn'orth....